Research On Macroscopic And Microscopic Deformation And Damage Behaviors In Helical Rolling Forming Of The Ball Bearing's Rolling Elements

The rolling bearing is one of the key parts for the major equipment fields of high-speed railway, high-speed precise machine, and metallurgy mill. However, the current domestic production of rolling bearings can't fully meet the high-speed, heavy-duty and other harsh service conditions in the above areas. As a key component of rolling bearing, the forming manufacturing technology level of rolling elements has direct influences on the dynamic performance, reliability and service life of rolling bearings. The helical rolling process is a high-quality and high-efficiency plastic processing technology for the production of rolling elements. Due to the complexity of process design and deformation mechanisms, and the lack of scientific regulation methods for forming precision and performance, the helical rolling process can't be effectively serviced for the production of high-performance rolling elements.In this study, taking the hot helical rolling process of steel-ball rolling elements as the study object, the 3D coupled macroscopic and microscopic behaviors finite element model was established under SIMUFACT software environment after successfully solving the key problems of roll's precision modeling, workpiece distortion, meshing technology and definition of solving parameters. Based on the simulation results, the distribution and evolution laws of macroscopic thermodynamic and microstructure were revealed, such as plastic strain, temperature, rolling force, relative sliding, tool wear, dynamic recrystallization, static recrystallization and grain size.According to the research of stress distribution and evolution laws, it can be concluded that the central damage is the combination result of high-level transverse tensile stress, cycle alternating shear stress and negative hydrostatic stress caused by multi-tensile stresses. Considering the above damage causes, the traditional Lemaitre damage model was improved by without considering the damage growth under negative hydrostatic stress state and coupling the effects of deformation temperature and strain rate based on the Zener-Hollomon coefficient. Moreover, with the help of secondary development technology of SIMUFACT software, the damage prediction of the helical rolling process for steel-balls was achieved after embedding the improved damage model into finite element model.Though studying the effect mechanisms of different groove characteristics and rolling parameters on helical forming of steel-balls, some significant conclusions were obtained. The proposed groove scheme of power exponential function curve for rib height changing characteristic can get a higher forming accuracy and finer grain size. Excessively high or low rolling temperature and excessively large or small cross angle can both lead to a lower forming accuracy. The grain size and central damage of rolling balls are sensitive to the rolling temperature, which significantly increase with the rising of rolling temperature. The above results can provide an effective guide for the shape-controlling and performance-controlling forming of steel-ball rolling elements during hot helical rolling process.